If you use this map and zoom in to the Blue mountains area immediately west of Sydney you can see the extent of the burn so far.
http://www.rfs.nsw.gov.au/dsp_content.cfm?cat_id=683
The "State Mine" fire looks like its taken over 1/3rd of the same area as Sydney's metropolitan area. That's about the same size as London North of the Thames to the M25!